Methods and systems for positioning a specimen and characterizing an x-ray beam incident onto the specimen in a Transmission, Small-Angle X-ray Scatterometry (T-SAXS) metrology system are described herein. A specimen positioning system locates a wafer vertically and actively positions the wafer in six degrees of freedom with respect to the x-ray illumination beam without attenuating the transmitted radiation. In some embodiments, a cylindrically shaped occlusion element is scanned across the illumination beam while the detected intensity of the transmitted flux is measured to precisely locate the beam center. In some other embodiments, a periodic calibration target is employed to precisely locate the beam center. The periodic calibration target includes one or more spatially defined zones having different periodic structures that diffract X-ray illumination light into distinct, measurable diffraction patterns.
Legal claims defining the scope of protection, as filed with the USPTO.
1. A metrology system comprising: an x-ray illumination source configured to generate an x-ray illumination beam incident on a semiconductor wafer; a specimen positioning system configured to actively control a position of the semiconductor wafer in six degrees of freedom with respect to the x-ray illumination beam, wherein a vector normal to a surface of the wafer is approximately perpendicular to a direction of a gravitational force imposed on the semiconductor wafer by gravity during measurement of the semiconductor wafer by the metrology system; an x-ray detector configured to detect a first amount of x-ray radiation from the semiconductor wafer in response to the incident x-ray illumination beam; and a computing system configured to determine a value of a parameter of interest characterizing a structure disposed on the semiconductor wafer.
2. The metrology system of claim 1 , the specimen positioning system comprising: a base frame; a stage reference frame configured to rotate with respect to the base frame about an axis of rotation that is perpendicular to the illumination beam and approximately parallel to the wafer surface; a wafer stage mounted to stage reference frame, the wafer stage configured to locate the wafer with respect to the incident illumination beam at any desired location over an active area of the semiconductor wafer; a three axis stage mounted to the wafer stage configured to move the semiconductor wafer in a direction approximately aligned with the illumination beam and to rotate the semiconductor wafer about two orthogonal axes of rotation, both approximately perpendicular to the illumination beam; and a rotary stage mounted to the three axis stage, the rotary stage configured to rotate the wafer about an axis approximately normal to the wafer surface.
3. The metrology system of claim 2 , wherein the wafer stage and the three axis stage are mechanically coupled by six points of mechanical contact arranged in a kinematic coupling.
4. The metrology system of claim 1 , the specimen positioning system comprising one or more sensors configured to measure a location of a back-side surface of the semiconductor wafer with respect to the specimen positioning system in a direction approximately normal to the wafer surface, one or more sensors configured to measure a location of a front-side surface of the semiconductor wafer with respect to the specimen positioning system in a direction approximately normal to the wafer surface, or a combination thereof.
5. The metrology system of claim 2 , the specimen positioning system comprising one or more edge gripper devices configured to mechanically couple the semiconductor wafer to the rotary stage at the edges of the semiconductor wafer.
6. The metrology system of claim 1 , the specimen positioning system comprising a rotary counterweight disposed on the stage reference frame, wherein a center of mass of the stage reference frame configured to rotate with respect to the base frame about the axis of rotation is approximately aligned with the axis of rotation.
7. The metrology system of claim 1 , further comprising: a first vacuum chamber enveloping a significant portion of an illumination beam path between the x-ray illumination source and the semiconductor wafer.
8. The metrology system of claim 1 , further comprising: a first vacuum chamber enveloping a significant portion of a collection beam path between the semiconductor wafer and the x-ray detector.
9. A metrology system comprising: an x-ray illumination subsystem configured to generate an x-ray illumination beam; a specimen positioning system configured to position a specimen with respect to the x-ray illumination beam such that the x-ray illumination beam is incident on the surface of the specimen at any location on the surface of the specimen and rotate the specimen with respect to the x-ray illumination beam about an axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of angles of incidence and rotate the specimen about an azimuth axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of azimuth angles; a beam occlusion calibration target including a cylindrical pin and one or more markers disposed in a plane aligned with a central axis of the cylindrical pin; an x-ray detector configured to detect an amount of transmitted flux over a range of positions of the specimen positioning system, wherein at least a portion of the x-ray illumination beam is incident on the cylindrical pin over the range of positions; and a computing system configured to determine a location of incidence of the x-ray illumination beam with respect the specimen positioning system based on the detected amount of transmitted flux.
10. The metrology system of claim 9 , wherein the range of positions includes a range of angles of incidence, and wherein the computing system is further configured to determine an adjustment of a position of the axis of rotation with respect to the x-ray illumination beam to align the axis of rotation and the x-ray illumination beam.
11. The metrology system of claim 10 , wherein the determining of the adjustment of the position of the axis of rotation with respect to the x-ray illumination beam is based on the detected amount of transmitted flux.
12. The metrology system of claim 10 , further comprising: an alignment camera that generates a plurality of images of at least a portion of the one or more markers or one or more markers disposed on the specimen at a plurality of different angles of incidence, and wherein a misalignment of the position of the axis of rotation with respect to the one or more markers or the one or more markers disposed on the specimen is determined based on a displacement of the one or more markers or the one or more markers disposed on the specimen measured in the plurality of images.
13. The metrology system of claim 10 , further comprising: one or more actuators configured to adjust a position of one or more elements of the x-ray illumination subsystem to adjust the position of the axis of rotation with respect to the x-ray illumination beam.
14. The metrology system of claim 10 , further comprising: one or more actuators configured to adjust the position of specimen positioning system with respect to the x-ray illumination beam to align the axis of rotation and the x-ray illumination beam.
15. The metrology system of claim 9 , wherein the determining of the location of incidence of the x-ray illumination beam with respect the specimen positioning system is based on a model of transmitted flux as a function of position of the cylindrical pin with respect to the x-ray illumination beam.
16. The metrology system of claim 9 , further comprising: an alignment camera that generates an image of at least a portion of the marker, wherein the computing system is further configured to locate the marker in the coordinate system of the specimen positioning system based on the image and estimate a location of incidence of the x-ray illumination beam in the coordinate system of the specimen positioning system based on the location of the marker and a known distance between the marker and the cylindrical pin.
17. The metrology system of claim 16 , wherein the alignment camera generates an image of at least one fiducial marker disposed on the specimen, and wherein the computing system is further configured to locate the fiducial marker in the coordinate system of the specimen positioning system based on the image.
18. The metrology system of claim 17 , wherein the alignment camera rotates about the axis of rotation with the specimen.
19. The metrology system of claim 9 , further comprising: one or more sensors configured to measure a location of a back-side surface of the specimen with respect to the specimen positioning system in a direction approximately normal to the wafer surface, one or more sensors configured to measure a location of a front-side surface of the specimen with respect to the specimen positioning system in a direction approximately normal to the wafer surface, or a combination thereof.
20. The metrology system of claim 9 , wherein the beam occlusion calibration target is disposed on the specimen positioning system or the specimen.
21. The metrology system of claim 9 , further comprising: a first vacuum chamber enveloping a significant portion of an illumination beam path between the x-ray illumination source and the specimen.
22. The metrology system of claim 9 , further comprising: a first vacuum chamber enveloping a significant portion of a collection beam path between the specimen and the x-ray detector.
23. A metrology system comprising: an x-ray illumination source configured to generate an x-ray illumination beam; a specimen positioning system configured to position a specimen with respect to the x-ray illumination beam such that the x-ray illumination beam is incident on the surface of the specimen at any location on the surface of the specimen and rotate the specimen with respect to the x-ray illumination beam about an axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of angles of incidence and rotate the specimen about an azimuth axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of azimuth angles, wherein each of the plurality of angles of incidence describes an angle between the x-ray illumination beam and the surface of the specimen; a periodic calibration target including one or more periodic structures of known extent on the periodic calibration target and one or more markers disposed in a plane aligned with the one or more periodic structures; an x-ray detector configured to detect an amount of transmitted flux over a range of positions of the specimen positioning system, wherein at least a portion of the x-ray illumination beam is incident on the one or more periodic structures over the range of positions; and a computing system configured to determine a location of incidence of the x-ray illumination beam with respect the specimen positioning system based on the detected amount of transmitted flux.
24. The metrology system of claim 23 , wherein the range of positions includes a range of angles of incidence, and wherein the computing system is further configured to determine an adjustment of a position of the axis of rotation with respect to the x-ray illumination beam based on the detected amount of transmitted flux.
25. The metrology system of claim 23 , wherein the periodic calibration target includes a boundary line between two periodic structures that differ in periodicity, orientation, or both.
26. The metrology system of claim 23 , wherein the periodic calibration target includes an intersection point among three of more periodic structures that differ in periodicity, orientation, or both.
27. The metrology system of claim 23 , wherein the periodic calibration target is disposed on the specimen positioning system or the specimen.
28. A method comprising: generating an x-ray illumination beam by an x-ray illumination subsystem; positioning a specimen with respect to the x-ray illumination beam such that the x-ray illumination beam is incident on the surface of the specimen at any location on the surface of the specimen; rotating the specimen with respect to the x-ray illumination beam about an axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of angles of incidence, wherein each of the plurality of angles of incidence describes an angle between the x-ray illumination beam and the surface of the specimen; rotating the specimen about an azimuth axis of rotation such that the x-ray illumination beam is incident on the surface of the specimen at any location at a plurality of azimuth angles; illuminating a calibration target with the x-ray illumination beam, the calibration target including one or more markers; detecting an amount of transmitted flux over a range of positions of the specimen positioning system, wherein at least a portion of the x-ray illumination beam is incident on the calibration target over the range of positions; and determining a location of incidence of the x-ray illumination beam with respect the specimen positioning system based on the detected amount of transmitted flux.
29. The method of claim 28 , further comprising: determining an adjustment of a position of the axis of rotation with respect to the x-ray illumination beam to align the axis of rotation and the x-ray illumination beam, wherein the range of positions includes a range of angles of incidence.
30. The method of claim 29 , wherein the determining of the adjustment of the position of the axis of rotation with respect to the x-ray illumination beam is based on the detected amount of transmitted flux.
31. The method of claim 29 , further comprising: generating a plurality of images of at least a portion of the one or more markers or one or more markers disposed on the specimen at a plurality of different angles of incidence, wherein a misalignment of the position of the axis of rotation with respect to the one or more markers or the one or more markers disposed on the specimen is determined based on a displacement of the one or more markers or the one or more markers disposed on the specimen measured in the plurality of images.
32. The method of claim 29 , further comprising: adjusting a position of one or more elements of the x-ray illumination subsystem to adjust the position of the axis of rotation with respect to the x-ray illumination beam.
33. The method of claim 29 , further comprising: adjusting the position of specimen positioning system with respect to the x-ray illumination beam to align the axis of rotation and the x-ray illumination beam.
34. The method of claim 28 , wherein the calibration target includes one or more periodic structures of known extent, and wherein the one or more markers are disposed in a plane aligned with the one or more periodic structures.
35. The method of claim 28 , wherein the calibration target includes a cylindrical pin, wherein the one or more markers are disposed in a plane aligned with a central axis of the cylindrical pin.
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May 9, 2018
July 27, 2021
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